In typical thermal printers, a resistive element thermal head is used to transfer dye from a dye bearing donor web to a dye receiving member. The head, dye donor and receiver are brought into contact, and the thermal head elements are selectively energized to transfer variable quantities of thermal dye from the donor to the receiver. The receiver is advanced past the thermal head in a controlled manner so that sequential lines of pixels are generated until a complete image is formed on the dye receiver. The transferred dye remains close to the surface of the receiver and is susceptible to mechanical, chemical and thermal aging and deterioration. Increased printing speed is always desirable, but as a result, the dye image becomes even more susceptible to damage. In addition, mechanical deformation occurs in the print as speed increases and the quantity of dye increases. Accordingly, it will be appreciated that it would be highly desirable to repair the damage and provide greater stability of the resulting image.
There are several ways to improve the image stability after printing. In some printing processes, the dyes are reheated by rollers that apply a controlled amount of heat to the image bearing surface. As a result of the heating process, the thermal dyes migrate a greater distance into the dye receiver surface and image stability is improved. While this process tends to improve dye stability, it does not repair mechanical damage to the print surface.
U.S. Pat. No. 4,666,320 which issued May 19, 1987 to Kobayashi et al. discloses that repeating the thermal printing process using a non-inked web in the printing station improves dye stability and improves mechanical defects in the surface, and that a protective coating can be applied in the clear area to provide a surface coating over the inked area. U.S. Pat. No. 5,027,160 which issued Jun. 25, 1991 to Okada et al. discloses an image fixing apparatus that includes a heater and an endless film through which a toner image on a recording material is heated by heat produced by the heater. Unfortunately, it is difficult to maintain the constant temperatures that are required for high quality fusing. Accordingly, it will be appreciated that it would be highly desirable to have a fusing apparatus that provides even, constant temperature heat for fusing.